.\"
.\" Copyright (c) 2000 Alfred Perlstein
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.Dd November 15, 2000
.Dt ACCF_HTTP 9
.Os
.Sh NAME
.Nm accf_http
.Nd "buffer incoming connections until a certain complete HTTP request arrives"
.Sh SYNOPSIS
.Nm options INET
.Nm options ACCEPT_FILTER_HTTP
.Nm kldload accf_http
.Sh DESCRIPTION
This is a filter to be placed on a socket that will be using
.Fn accept
to receive incoming HTTP connections.
.Pp
It prevents the application from receiving the connected descriptor via
.Fn accept
until either a full HTTP/1.0 or HTTP/1.1 HEAD or GET request has
been buffered by the kernel.
.Pp
If something other than a HTTP/1.0 or
HTTP/1.1 HEAD or GET request is received the kernel will
allow the application to receive the connection descriptor
via
.Fn accept .
.Pp
The utility of
.Nm
is such that a server will not have to context switch several times
before performing the initial parsing of the request.
This effectively reduces the amount of required CPU utilization
to handle incoming requests by keeping active
processes in preforking servers such as Apache low
and reducing the size of the file descriptor set that needs
to be managed by interfaces such as
.Fn select ,
.Fn poll
or
.Fn kevent
based servers.
.Pp
The
.Nm
kernel option is also a module that can be enabled at runtime via
.Xr kldload 8
if the INET option has been compiled into the kernel.
.Sh EXAMPLES
Assuming ACCEPT_FILTER_HTTP has been included in the kernel config
file or the
.Nm
module
has been loaded, this will enable the http accept filter
on the socket
.Fa sok .
.Bd -literal -offset 0i
	struct accept_filter_arg afa;

	bzero(&afa, sizeof(afa));
	strcpy(afa.af_name, "httpready");
	setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
.Ed
.Sh SEE ALSO
.Xr setsockopt 2 ,
.Xr accept_filter 9
.Sh HISTORY
The accept filter mechanism and the
accf_http filter were introduced in
.Fx 4.0 .
.Sh AUTHORS
This manual page and the filter were written by
.An Alfred Perlstein .
